The present invention relates to an electric discharge tube used as an artificial light source for photographic, and particularly to a discharge tube having a durability to an electric input for light emission, and a strobe device and a camera including the tube.
An electric discharge tube used as an artificial light source incorporated in a photographic strobe device or photographic camera is required to be have a small size and a large light emission capacity for portable use. Such discharge tube includes a glass bulb and a pair of main electrodes, i. e., an anode and a cathode, provided at both ends of the glass tube and is filled with rare gas. The discharge tube discharges to emit light by an electric input supplied between the main electrodes.
The amount of the emitted light increases as the electric input is larger, as known well, and the requirement needs a decrease of the size of the glass bulb and an increase of the electric input. However, the increase and the decrease is limited. An electric input exceeding its limit may crack or break the glass bulb with a smaller number of light emissions, and hence, the excessive electric input cannot be applied.
An electric discharge tube having a large strength of glass bulb and an enhanced durability to the electric input is disclosed in Japanese Patent Laid-Open Publication No.62-206761. This discharge tube includes a thin film of silicon dioxide formed on inner and outer surfaces of a glass bulb, and hence has an enhanced strength of the glass bulb to an electric input for light emission without including a quartz tube having a large strength.
The strength to the electric input applied to the discharge tube is influenced by various factors. Therefore, the thin film of silicon dioxide on the inner and outer surfaces of the glass bulb may not provide the discharge tube having the enhanced strength of the glass bulb by itself.
In addition, the discharge tube is recently demanded to have a small size. The increase of the strength of the glass bulb allows the discharge tube to have the small size, and accordingly provides a photographic strobe device and a photographic camera having small sizes.
An electric discharge tube can withstand a large electric input, and have s small size. The discharge tube provides a photographic strobe device and a photographic camera having small sizes. The discharge tube includes a glass bulb having a wall thickness of 0.2 mm to 0.6 mm and filled with rare gas, a pair of main electrodes provided at both ends of the glass bulb, respectively, a trigger electrode formed on an outer surface of the glass bulb, and a film of silicon dioxide having a thickness of 0.05 to 0.11 xcexcm and formed inside of the glass bulb. An electric power not larger than 0.90 Ws/mm3 with respect to an inner volume of the glass bulb is applied to the main electrodes.